1. Field of the Invention
This invention relates to systems for measuring conductivity of bodily fluids, in general, and to an electrical system for automatically measuring hematocrit and giving an approximation of hemoglobin, in particular.
2. Background of the Prior Art
Various methods and apparatus are known for studying liquid samples. Some involve centrifugation, others utilize agitation, and there are still others which depend upon the electrical characteristics of the sample being tested. In virtually all of these known techniques, especially those in the medical field, it is of prime importance to maintain isolation between samples. A still further problem relates to the protection of the technician against contracting infectious diseases from the samples under test. With the known methods and apparatus, very little protection is afforded.
An example of an apparatus for studying the electrical characteristics of blood can be found in U.S. Pat. No. Re. 30,007, issued to Steuer et al on May 22, 1979. This apparatus includes a rod-like probe having two conductive electrodes at the tip of the probe. A blood sample is associated with the electrodes of the probe, and an electrical current is applied across the blood for the purpose of hematocrit determinations. Obviously, the probe must be thoroughly cleaned between tests to ensure accurate test results.
An example of a disposable blood sample card is shown in U.S. Pat. No. 4,123,701, filed on July 1, 1976, to inventors Josefson and Veth, and assigned to United States Surgical Corporation. The blood sample card described therein is a disposable blood sample carrier comprising a substantially planar base portion made of an electrically insulating material. The card is sterilized, pre-packaged and disposable after a single use. In the base portion of the card is a well to receive the blood sample. The well is sized so as to accommodate approximately one drop of blood, and a well volume on the order of 0.05 ml is described. Electrodes are positioned in the well and are adapted to be connected to an instrument that evaluates the electrical characteristics of the blood sample by means of electrical circuitry, as disclosed, for example, in the aforementioned U.S. Pat. No. Re. 30,007.
The measuring instrument and blood sample card just described, are considered to be exemplary of the present state of the art. Nevertheless, there is a need for a system which provides a simplified, safe and accurate electrical evaluation of liquid samples. The present invention is directed toward filling that need.